Eddy current speed reducer

Abstract

An eddy current braking apparatus according to the invention comprises: a brake disk (2) connected to a rotary shaft (1); a plurality of permanent magnets (7) arranged so that magnetic pole surfaces are opposed to the brake disk (2); and a drive mechanism for moving the permanent magnets (7) toward and away from the brake disk (2). Preferably, it further comprises a guide sleeve (3) supported by a nonrotatable structural section not connected to the rotary shaft (1), which receives a support ring (4) supporting the permanent magnets (7) and is arranged facing to the brake disk (2). Moreover, in the guide sleeve (3), there are provided ferromagnetic members (8) positioned opposite to the brake disk (2). Alternatively, the whole of said guide sleeve (3) including an end face opposed to said permanent magnets (7) is constructed of nonmagnetic material.

Description

TECHNICAL FIELD [0001] The present invention relates to an eddy current braking apparatus which assists a main brake installed in a vehicle or the like, and relates specifically to an eddy current braking apparatus using a disk type brake member. BACKGROUND ART [0002] Braking apparatus for vehicles such as trucks and buses include, in addition to primary braking apparatus such as foot brakes and auxiliary braking apparatus such as exhaust brakes, eddy current braking apparatus which reduce speed in a stable manner, and also prevent the foot brake from burning out, in such situations as when descending long slopes. [0003]FIG. 4 is a diagram showing the structure of an eddy current braking apparatus as proposed in Japanese Examined Patent Publication No. Hei. 6-81486, which shows an example of a method in which the polar surfaces (magnetic pole surfaces) of permanent magnets are in an opposed relationship to a rotary drum type braking member. The present specification may describe thi...

AI Technical Summary

Benefits of technology

[0017] As described above, because with this system the permanent magnets oppose the brake disk and are moved towards it to generate braking torque in the disk itself, the magnetic lines of force of the permanent magnets can be applied to the brake disk with a short magnetic path length. Consequently, the magnetic resistance of the magnetic circuit is minimized, and the efficiency of braking torque generation is improved. As a result of the improved braking efficiency, comparatively small permanent magnets can be used, which allows a lighter, more compact and lower cost apparatus.

[0035] In addition, in the eddy current braking apparatus of the present invention, the guide sleeve may be constructed from a thin walled material. Because this allows the weight of the whole guide sleeve to be reduced, small and light-weighted apparatus can be realized. In this case, by partially reinforcing the guide sleeve, the strength of the guide sleeve can be maintained.

Problems solved by technology

However, the eddy current braking apparatus shown in FIG. 4 entails many problems, categorized as problems caused by the use of a rotary drum, and problems caused by employing the “opposing magnet pole surface method”.

First, a serious problem caused by the use of a rotary drum is that because the stator (guide sleeve) which houses the permanent magnets and the like is covered by the inner peripheral surface of the rotary drum, heat dissipation is poor, and the heat generated during actuation causes marked expansion.

On the other hand, problems caused by employing the “opposing magnet pole surface method” can be attributed to the moving of the support ring which arranges the permanent magnets closer to the inner peripheral surface of the rotary drum using the fluid pressure actuators.

In other words, in the proposed braking apparatus, the structure is such that the permanent magnets cannot be disposed on part of the inner circumference of the rotary drum, which makes it difficult to secure the necessary braking force.

Moreover, the length of the magnetic circuit formed by the permanent magnets may lengthen, and the magnetic circuit may be interrupted at a part of the inner peripheral surface, which reduce magnetic efficiency.

Furthermore, because this structure does not allow the permanent magnets to be disposed perpendicularly relative to the rotary drum and in an evenly spaced manner, a large stroke must be used to move the permanent magnets back to a non-braking position.

As described above, an eddy current braking apparatus using a rotary drum has problems with heat dissipation during braking, inherent in its structure.

Specifically, heat generated in the rotary drum during braking causes expansion of the outer peripheral section.

In order to absorb this expansion, a system of drum support that is complex in design is required, which complicates the drum sturucture.

In addition, because the rotational weight is concentrated towards the outside in the radial direction, it is difficult to adjust the rotational balance, and the excessive stress caused by centrifugal force causes such problems as a reduction in durability and a tendency for dimensional variation.

This means that the ability to use the components of the rotary drum as common parts is lost.

However, in the eddy current braking apparatus shown in FIG. 5, because the magnetic circuit is oblique during braking, the magnetic circuit lengthens, which increases the likelihood of a short in the magnetism.

This results in deterioration in the magnetic efficiency.

This also results in a deterioration in magnetic efficiency.

As a result, the braking apparatus itself must be larger, and a greater length of time is required to switch braking states.

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